Method for rendering flexible sheet material non-adherent

ABSTRACT

A solventless composition for rendering flexible sheet materials non-adherent to surfaces to which they normally adhere is disclosed. These compositions include a low viscosity vinyl chainstopped polysiloxane or a low viscosity silanol chainstopped polysiloxane with an organohydrogenpolysiloxane and a curing catalyst.

This is a division, of application Ser. No. 523,898, filed Nov. 14,1974, now abandoned.

This invention provides a solventless composition for rendering flexiblesheet materials non-adherent to surfaces to which they normally adhere.These compositions are based on a low viscosity vinyl chainstoppedpolysiloxane or a low viscosity silanol chainstopped polysiloxane withan organohydrogenpolysiloxane and a curing catalyst.

BACKGROUND OF THE INVENTION

In the prior art, silicone compositions have been employed as releaseagents for materials such as pressure sensitive adhesive systems. Theserelease agents have traditionally been solvent solutions or aqueousemulsions of reactive silicone polymers. Examples of these materials maybe found in U.S. Pat. Nos. 2,985,545 and 3,814,731 which are herebyincorporated by reference. One objection to these products is theproblem that is related to the solvent which is evaporated during thecuring stage. This solvent if vented to the atmosphere causes airpollution and this requires expensive solvent recovery equipment.Completely aqueous products present no pollution or solvent recoveryproblem but this type of product has had limited use for specializedapplications such as asphalt and latex packaging. The use of a solventhas always been considered necessary to reduce viscosity and to makehandling and coating of the silicone composition easier. Also, by properselection of the solvent, the highly reactive polysiloxanes have beenstabilized to give good shelf life to products that are normallyunstable.

It has now been found that a solventless polysiloxane composition can beformulated for rendering flexible sheet materials non-adherent tosurfaces to which they normally adhere. These compositions are based onthe use of a low viscosity vinyl chainstopped polysiloxane or a lowviscosity silanol chainstopped polysiloxane, anorganohydrogenpolysiloxane and a catalyst for curing the composition.This type composition may be applied to a paper substrate without theuse of a solvent. One method of applying this composition is by using asmooth roller followed by a doctor blade to remove excess composition.

DETAILED DESCRIPTION OF THE INVENTION

The solventless compositions of the invention which are useful forrendering flexible sheet materials non-adherent to surfaces whichnormally adhere thereto will comprise:

A. A VINYL CHAINSTOPPED POLYSILOXANE HAVING UNITS OF THE FORMULA:##EQU1## wherein R is a monovalent hydrocarbon radical, a halogenatedmonovalent hydrocarbon radical or a cyanoalkyl radical, a is 0 to 3, bis 0.005 to 2.0 and a plus b is 0.8 to 3 and said polysiloxane has aviscosity between 100 and 5000 cstks at 25° C; or a silanol chainstoppedpolysiloxane having the formula: ##STR1## wherein R is the same ashereinabove described and t has a value which will give a viscositybetween 100 and 5000 cstks.;

b. an organic hydrogenpolysiloxane of the formula: ##EQU2## wherein R, aand b are the same as hereinabove described; and

c. a catalyst for curing said composition.

The preferred type of vinyl chainstopped polysiloxanes are of theformula: ##STR2## wherein R and R¹ are free of unsaturation and aremonovalent hydrocarbon radicals, halogenated monovalent hydrocarbonradicals or cyanoalkyl radicals, with at least 50% of the R¹ groupsbeing methyl and n has a value sufficient to provide a fluid materialhaving a viscosity of from 100 to 5000 cstks. at 25° C, or morepreferably from 300 to 1000 cstks. at 25° C.

The substituents R and R¹ may be alkyl, e.g., methyl, ethyl, propyl,butyl, octyl, etc., aryl, e.g., phenyl, tolyl, xylyl, etc., cycloalkyl,e.g., cyclohexyl, cycloheptyl, etc., aralkyl, e.g., benzyl, phenethyl,etc., halogenated aryl, e.g., chlorophenyl, bromophenyl, chloronaphthyl,etc., cyanoalkyl, e.g., cyanoethyl, cyanopropyl, etc., or mixtures ofany of the foregoing. These materials are described in U.S. Pat. Nos.3,344,111 and in 3,436,366 which are both incorporated by reference.

The preferred catalysts for curing the vinyl chainstopped polysiloxaneand the organohydrogenpolysiloxane are platinum catalysts.

The platinum catalyst component employed in the present invention can beany of the well known platinum catalysts which are effective forcatalyzing the reaction between silicon-bonded vinyl groups. Thesematerials include the various finely divided elemental platinumcatalysts, such as those described in Bailey, U.S. Pat. No. 2,970,150,the chloroplatinic acid catalysts described in Speier, U.S. Pat. No.2,823,218, the platinum-hydrocarbon complexes described in Ashby, U.S.Pat. No. 3,159,601 and U.S. Pat. No. 3,139,662, as well as the platinumalcoholate catalysts disclosed in Lamoreaux, U.S. Pat. No. 3,220,972.Regardless of the type of platinum catalyst employed, the catalyst isused in an amount sufficient to provide from about 10⁻³ to 10⁻⁶ gramatoms of platinum per mole of silicon-bonded vinyl groups in thecomposition. On another basis, a useful range of catalyst will provideone platinum atom for each 100 to 1,000,000 silicon-bonded vinyl groupsin the vinyl chainstopped polysiloxane. Especially preferably, theplatinum catalyst will be present in an amount sufficient to providefrom 5 to 50 parts per million of platinum based on the weight of vinylchainstopped polyorganosiloxane component.

The preferred silanol chainstopped polysiloxanes are of the formula:##STR3## wherein R is a monovalent hydrocarbon radical and at least 50%of the R groups are methyl groups. The preferred silanol chainstoppedpolysiloxanes will have a viscosity of 300 to 1000 cstks. at 25° C.

The silanol chainstopped polysiloxanes are prepared by the equilibrationof cyclic polysiloxanes with an alkali metal hydroxide catalyst. Thedesired viscosity is obtained by controling the amount of water added tothe reaction. These procedures are described in the literature and arewell known to those skilled in the art.

The compositions which contain the silanol chainstopped polysiloxanesare cured with from 0.1-1% by weight of an organotin catalyst. Suitableorganotin compounds include dialkyl tin salts preferably dibutyl tinsalts such as dibutyl tin di-2-ethyl hexoate, dibutyl tin di-laurate,dibutyl tin diacetate and the like.

The organic hydrogenpolysiloxane can vary broadly in structure, and itmay comprise a mixture of materials. One characteristic is that it hasat least two silicon-bonded hydrogen atoms per molecule which act tocrosslink with the other polysiloxane component.

The organohydrogenpolysiloxane will preferably be of the formula:##EQU3## wherein R is as defined above, a is from 0 to 3, preferablyfrom 1.0 to 2.10, b is from 0.005 to 2.0, preferably from 0.1 to 1.0 andthe sum of a plus b is from 0.8 to 3, preferably 2.0 to 2.67. Theorganohydrogenpolysiloxane can be linear or cyclic in nature. Oneillustrative material is a linear dimethylhydrogen chainstoppeddimethylpolysiloxane containing from 2 to 3 silicon atoms in themolecule. Preferred materials will have a viscosity of 10-100 cstks. at25° C. Also, there may be employed methyl hydrogen polysiloxane ormultifunctional silanes such as methyl triacetoxysilane,trimethoxysilane, triethoxysilane, tetra-isopropoxysilane, andtriacetoxysilane, along with the hydrogen polysiloxane. Usually from 1to 10% by weight of the crosslinking organohydrogenpolysiloxane isrequired.

The catalyst may be precoated on the substrate and the coating bath mayconsist of the silanol or vinyl chainstopped polysiloxane andcrosslinking agent. This will extend the working life of the bath.

The vinyl chainstopped systems may be stabilized with from 100-500 ppm,preferably 200-400 ppm of acrylonitrile. The acrylonitrile will preventcuring of the composition until it is volatilized in the coatingoperation.

When the compositions of the invention are used to coat paper,depositions of about 0.25-1 lb/ream of paper will produce satisfactoryresults.

The preferred compositions will comprise the following components inparts by weight:

    ______________________________________                                        vinyl or silanol chain-                                                       stopped polysiloxane  5-20                                                    organic hydrogen                                                              polysiloxane          0.1-5                                                   catalyst              0.00001-1                                               ______________________________________                                    

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the process of the present invention.They are illustrative and the claims are not to be construed as limitingthereto.

EXAMPLE 1

The following materials were mixed and then applied to supercalenderedpaper with a knife coater at a deposition of about 1 lb/ream.

    ______________________________________                                                             Parts by weight                                          ______________________________________                                        Silanol stopped dimethylpolysiloxane                                          (500 cstks. at 25° C)                                                                         10                                                     Methyl hydrogen polysiloxane                                                                         1                                                      Dibutyl tin di-2-ethyl                                                        hexoate                .3                                                     ______________________________________                                    

The coated sheet was cured for 15 seconds at 300° C. The cured sheet wassmear-free and resistant to abrasion. An SBR adhesive was then appliedto the coating and laminated with a face stock. Release at 400 in./min.,was checked over a period of 2 months and found to remain a constant40-50 gms/in.

EXAMPLE 2

The following coating composition was prepared:

    ______________________________________                                                              Parts by weight                                         ______________________________________                                        Dimethylpolysiloxane, vinyl chain-                                            stopped (400 cstks. at 25° C)                                                                  10                                                    Methyl hydrogen polysiloxane                                                  (25 cstks. at 25° C)                                                                           0.5                                                   Acrylonitrile           0.004                                                 Platinum (5% platinum content                                                 of a solution of chloroplatinic                                               acid in n-butanol to give a concentration                                     by weight)              0.00005                                               ______________________________________                                    

The platinum catalyst was added to the vinyl chainstopped fluid andmixed well. The acrylonitrile was then added and mixed, and finally themethyl hydrogen polysiloxane was added and mixed. The resulting solutionwas then applied to supercalendered kraft paper as in Example 1. Thecoating was repeated and cured 15 seconds at 250° F. In each case, asmear-free coating was obtained which gave the same release as Example1.

EXAMPLE 3

The vinyl stopped dimethyl polymer in Example 2 was replaced by a vinylstopped fluid having a viscosity of 4000 cstks. at 25° C with the sameresults as in Example 2. Although the higher viscosity can be curedunder the same conditions as the lower, the lower viscosity is preferredsince it is easier to apply as a thin coating.

Obviously, many variations will suggest themselves to those skilled inthe art from the above detailed description without departing from thescope or spirit of the invention. It is, therefore, to be understoodthat changes may be made in the particular embodiments of the inventiondescribed which are within the full intended scope of the invention asdefined by the appended claims.

I claim:
 1. A method for rendering flexible sheet materials non-adherentto surfaces which normally adhere thereto, said method comprisingapplying to said flexible sheet material, an amount of a solventlesscomposition that will render said flexible sheet material non-adherentto surfaces which normally adhere thereto, said solventless compositioncomprising:a. from 5-20 parts by weight of a silanol chainstoppedpolysiloxane having the formula: ##STR4## wherein R is a monovalenthydrocarbon radical, a halogenated monovalent hydrocarbon radical or acyanoalkyl radical and t has a value which will give a viscosity between300 and 1,000 cstks. at 25° C; b. from 0.1 to 5 parts by weight of anorganic hydrogenpolysiloxane of the formula: ##EQU4## wherein R is thesame as hereinabove defined and a is 0 to 3, b is 0.005 to 2.0 and aplus b is 0.8 to 3.0; and a sufficient amount of a dialkyltin catalystfor curing said composition.
 2. A method as defined in claim 1 whereinfrom 0.00001 to 1 part by weight of the dialkyl tin catalyst is isemployed.
 3. A method for rendering flexible sheet materialsnon-adherent to surfaces which normally adhere thereto said methodcomprising:a. first applying to said flexible sheet material an amountof dialkyltin catalyst for curing a coating composition which comprises:i. a silanol chainstopped polysiloxane having the formula ##STR5##wherein R is a monovalent hydrocarbon radical, a halogenated hydrocarbonradical or a cyanoalkyl radical and t has a value which will give aviscosity between 300 and 1000 cstks. at 25° C; and ii. an organichydrogenpolysiloxane of the formula ##EQU5## wherein R is the same ashereinabove defined and a is 0 to 3, b is 0.005 to 2.0 and a plus b is0.8 to 3.0; b. applying said coating composition to the catalyzedflexible sheet and; c. curing said coating composition.
 4. A method asdefined in claim 3 wherein from 0.00001 to 1 part by weight of dialkyltin catalyst is employed.